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Tyrannosaurus View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Edinburgh Research Explorer Edinburgh Research Explorer A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia Citation for published version: Brusatte, SL, Carr, TD, Erickson, GM, Bever, GS & Norell, MA 2009, 'A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia' Proceedings of the National Academy of Sciences, vol 106, no. 41, pp. 17261-17266. DOI: 10.1073/pnas.0906911106 Digital Object Identifier (DOI): 10.1073/pnas.0906911106 Link: Link to publication record in Edinburgh Research Explorer Document Version: Publisher's PDF, also known as Version of record Published In: Proceedings of the National Academy of Sciences Publisher Rights Statement: Gold Open Access. Published by the National Academy of Sciences - PNAS (2009) General rights Copyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy The University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 28. Apr. 2017 A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia Stephen L. Brusattea,b,1, Thomas D. Carrc, Gregory M. Ericksona,d, Gabe S. Bevera, and Mark A. Norella aDepartment of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024; bDepartment of Earth and Environmental Sciences, Columbia University, New York, NY; cDepartment of Biology, Carthage College, 2001 Alford Park Drive, Kenosha, WI 53140; and dDepartment of Biological Science, 319 King Building, Florida State University, Tallahassee, FL 32306-4295 Edited by Paul E. Olsen, Lamont–Doherty Earth Observatory of Columbia University, Palisades, NY, and approved September 8, 2009 (received for review June 19, 2009) Tyrannosaurid theropods are characterized by a generalized body ulated skull that allows for meticulous observation of tyranno- plan, and all well-known taxa possess deep and robust skulls that saurid cranial anatomy. This new tyrannosaur is small-bodied are optimized for exerting powerful bite forces. The fragmentary and possesses a bizarre long-snouted and gracile skull with eight Late Cretaceous Alioramus appears to deviate from this trend, but discrete horns, an unusual cranial form for a Late Cretaceous its holotype and only known specimen is incomplete and poorly tyrannosaurid. It is extremely similar to, and shares many unique described. A remarkable new tyrannosaurid specimen from the characters with, the holotype of A. remotus, but it is also Maastrichtian (Late Cretaceous) of Mongolia, including a nearly distinguishable by numerous characters and thus is referred to as complete and well-preserved skull and an extensive postcranium, a new species of Alioramus. The new specimen helps clarify the represents a new species of Alioramus, Alioramus altai. This spec- body form and systematic affinities of this long-enigmatic genus, imen conclusively demonstrates that Alioramus is a small, gracile, which is now strongly placed as a derived tyrannosaurid closely long-snouted carnivore that deviates from other tyrannosaurids in related to Tyrannosaurus. Thus, Alioramus is a small, sleek, its body plan and presumably its ecological habits. As such, it longirostrine tyrannosaurid, which lived alongside the mega- increases the range of morphological diversity in one of the most predatory Tarbosaurus. familiar extinct clades. Phylogenetic analysis places Alioramus deep within the megapredatory Tyrannosauridae, and within the Systematic Paleontology. Theropoda Marsh, 1881; Tetanurae tyrannosaurine subclade that also includes Tarbosaurus and Tyr- Gauthier, 1986; Coelurosauria Huene, 1914; Tyrannosauroidea annosaurus. Both pneumatization and ornamentation are extreme Osborn, 1905; Tyrannosauridae Osborn, 1905; Tyrannosaurinae compared with other tyrannosaurids, and the skull contains eight Osborn, 1905; Alioramus Kurzanov, 1976; Alioramus altai, sp. nov. discrete horns. The new specimen is histologically aged at nine years old but is smaller than other tyrannosaurids of similar age. Holotype. Institute of Geology, Mongolia (IGM), Ulaan Baatar Despite its divergent cranial form, Alioramus is characterized by a 100/1844 is a substantially complete skeleton found associated similar sequence of ontogenetic changes as the megapredatory and belonging to a single individual that includes a nearly EVOLUTION Tyrannosaurus and Albertosaurus, indicating that ontogenetic complete and disarticulated skull and is missing the forelimbs, change is conservative in tyrannosaurids. regions of the hindlimbs, the pubes, and much of the dorsal and caudal vertebral series (Figs. 1–3 and Tables S1–S3). Dinosauria ͉ heterochrony ͉ Tyrannosauridae ͉ Theropoda ͉ pneumaticity Etymology. Altai is in reference to the Altai mountain range, a he colossal predator Tyrannosaurus is undoubtedly the most prominent topographic feature of southern Mongolia. Trecognizable dinosaur. Tyrannosaurus and several close rel- GEOLOGY atives are grouped together within Tyrannosauridae, a derived Horizon and Locality. The specimen was collected in 2001 at clade of large-bodied theropods that were the apex predators in Tsagaan Khushuu (originally called Tsagaan Uul) (10). These most terminal Cretaceous ecosystems in North America and beds are part of the Maastrichtian Nemegt Formation, which Asia (1–3). Tyrannosaurids are characterized by a general body crops out extensively at a number of localities in the area. The plan: All well-known species possess deep skulls, peg-like teeth, type locality for A. remotus, Nogon-Tsav, is often referred to as and robust lower jaws as adults, features thought to relate to a Nemegt equivalent, but detailed correlations have yet to be powerful bite forces and an unusual ‘‘puncture-pull’’ feeding undertaken, and faunal differences suggest that Tsaagan style in which the teeth penetrate through bone (4–6). As such, Khushuu and Nogon-Tsav may be different in age (10). these animals can be referred to as ‘‘megapredators.’’ One enigmatic tyrannosaurid, Alioramus remotus from the Diagnosis. A. altai is a tyrannosaurid theropod possessing the Late Cretaceous of Mongolia, appears to deviate from this trend following autapomorphies: an accessory pneumatic fenestra (7). The fragmentary holotype and only known specimen seems posterodorsal to promaxillary fenestra of maxilla; enlarged and to represent a long-snouted and gracile predator with an extreme degree of cranial ornamentation, but further details of its elongated maxillary fenestra (length:depth ratio of 1.9); a lat- anatomy, biology, and phylogenetic relationships have proven erally projecting horn on the jugal; a thick ridge on the dorsal controversial. Some phylogenetic analyses place A. remotus deep surface of the ectopterygoid; a palatine pneumatic recess ex- within the radiation of Asian tyrannosaurids (8), whereas other studies find it as a basal taxon outside of Tyrannosauridae (1, 2; Author contributions: S.L.B., T.D.C., G.M.E., G.S.B., and M.A.N. designed research; S.L.B., phylogenetic definitions following ref. 9). Furthermore, some T.D.C., G.M.E., and G.S.B. performed research; T.D.C. and G.M.E. contributed new reagents/ authors have suggested that the holotype of A. remotus is a analytic tools; S.L.B., T.D.C., G.M.E., G.S.B., and M.A.N. analyzed data; and S.L.B., T.D.C., juvenile and possibly an immature Tarbosaurus (3). These de- G.M.E., G.S.B., and M.A.N. wrote the paper. bates are difficult to resolve with the fragmentary holotype The authors declare no conflict of interest. material. This article is a PNAS Direct Submission. We report the discovery of a peculiar new tyrannosaurid from 1To whom correspondence should be addressed. E-mail: [email protected]. the Late Cretaceous of Mongolia that is known from a remark- This article contains supporting information online at www.pnas.org/cgi/content/full/ ably complete and well-preserved skeleton, including a disartic- 0906911106/DCSupplemental. www.pnas.org͞cgi͞doi͞10.1073͞pnas.0906911106 PNAS ͉ October 13, 2009 ͉ vol. 106 ͉ no. 41 ͉ 17261–17266 Fig. 1. Skull reconstruction of A. altai, based on the holotype (IGM 100/1844) and photos of individual bones of the holotype. (A) Left maxilla in lateral view. (B) Left nasal in lateral view. (C) Left lacrimal in lateral view. (D) Left jugal in lateral and dorsal views. (E) Left dentary in lateral view. apf, accessory promaxillary fenestra; cp, cornual process of jugal; jh, jugal horn; lh, lacrimal hornlet; nr, nasal rugosities. (Scale bars, 5 cm.) tending posteriorly beyond the posterior margin of the vomer- fenestrae, low and indistinct lacrimal horns, low nasal rugosities, opterygoid process; 20 dentary alveoli; an anteroposteriorly a larger postorbital horn, and a considerably lower tooth count elongate anterior mylohyoid foramen of the splenial; a thin in the maxilla and dentary (11, 12). epipophysis on the atlantal neurapophysis that terminates at a sharp point; a pneumatic pocket on the anterior surface of the Description
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